The Platform Documentation menu item points to a readme.html page.
The content of the page is as follows:

--------START_OF_readme.html------
All documentation for JBoss Enterprise Web Platform 5.1, including Release Notes, is available from:
http://access.redhat.com

Select JBoss Enterprise Web Platform < 5.0 from the sidebar for a full list of documentation available with JBoss Enterprise Web Platform 5.0 and its patch releases.
--------END_OF_readme.html------

I suppose all mentions of 5.0 should be changed to 5.1. I might be wrong. Right now there is no JBoss Enterprise Web Platform whatsoever in the customer portal.
Also, in the installer of EAP 5.1 the menu item points to http://www.redhat.com/docs/en-US/JBoss_Enterprise_Application_Platform/, so why is this different? Shouldn't both EAP and EWP take a similar approach?